This invention relates to pressure regulating apparatus for use with vehicle tires and particularly to a pressure regulator which can be set to regulate the pressure in the vehicle tire by adjusting the biasing force of a spring which urges a valve member to close an inlet port from a pressure source.
It is known to provide a valve mechanism wherein a spring, which normally biases a closure member towards a valve seating, is adjustable to regulate the pressure passing into the valve through an air inlet port. Such adjustment may be made by means of a screw threaded into part of the valve housing and acting on one end of the spring. Rotation of the screw in one direction or another thus increases or decreases the biasing force of the spring.
Such pressure regulators are disclosed in British patent specifications numbers 1567402, 138694, 336624, 384760, 1580240 and U.S. Pat. Nos. 2,690,757, 2,987,071, 4,869,306 and 4,883,107.
It is also known from British patent specification 8172/1910 to provide a spring biased pressure relief valve wherein the spring is located between a bridging member and the valve head, and where the biasing force of the spring is adjustable by moving the bridge member upwardly or downwardly with respect to the spring. The bridging member locates in slots in the valve housing and is secured in its desired position by means of nuts.
British patent specification 2215438-A shows a spring biased relief valve wherein a pin extends transversely form a plunger which is in engagement with the spring and the pin is engaged by a rotary camming face formed in part of the valve housing. Rotation of the plunger causes a camming action on the plunger to adjust the biasing force of the spring.
In all the above patent specifications the adjustment of the tire pressure is a slow operation.
There is, however, a need particularly in the case of military vehicles, e.g. personnel carriers operating in desert conditions or other soft or boggy terrain to be able to adjust the tire pressure downwardly with a great degree of urgency and accuracy.
In some circumstances a vehicle may suddenly arrive at an area of such difficult terrain and it is important to be able to either advance or withdraw without undue delay. Thus, in order to combat the effect of the ground conditions, there is a need to quickly lower the tire pressure in order to provide a "footprint" of larger area to increase the traction of the vehicle.